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Cool and warm season grasses provide options for producers planting irrigated pastures

by Wyoming Livestock Roundup

“There has been a renewed interest in irrigated pasture,” said Jerry Volesky, in a University of Nebraska webinar recorded in December 2014.

He noted that 2014 had strong pasture demand and low grain commodity prices. 

Warm, cool-season grass

“Producers have the option of either warm-season or cool-season grasses for perennials in irrigated pasture,” he explained.

Cool-season grasses usually begin growth in the spring, late March to early April, with rapid growth in May and early June.

“They will decline in growth rate in the warm summer months and pick up again a little in the fall, when temperatures cool down,” said Volesky.

Warm season grasses usually show initial growth in May, with the most rapid growth in late June and early July.

“By early September, warm-season grasses have mostly completed their growth for the season,” he stated.

He also noted that they go into dormancy soon after the season’s first frost.

“Overall, we tend to see more cool-season grasses used in irrigated pasture,” he said.


One standard mix that has been successful contains orchard grass, meadow brome, smooth brome and creeping foxtail. Including alfalfa or another legume is also an option.

“Wheatgrasses, in general, have very good spring production compared to some of the other cool-season grasses, but they don’t produce as well in the heat of the summer,” he said.

Rye grasses, Volesky observed, establish easily and quickly and have long-term persistence.

“I tend to favor mixtures over a single species,” he stated.

“Mixtures have advantages over a monoculture because there is better adaptability to soil conditions or moisture across a field.”

Also, different species have different growth patterns throughout the season, as well as variation in insect and disease resistance, persistence and winter hardiness, he explained.

Grass growth

“Another important point is the growth form of these grasses, such as bunchgrass versus sod-forming grasses,” said Volesky.

He noted that it is important to have a good mix of both types in irrigated pasture.

“There are number of commercially available seed mixes,” he said.

Using one example, he notes a combination of 75 percent meadow grass with 25 percent orchard grass.

“Orchard grass has a relatively small seed, so the number of seeds per pound will be different than the meadow grass. This mix will likely grow a 50 percent meadow grass and 50 percent orchard grass forage,” he explained.


Volesky also suggested incorporating legumes to help maintain nitrogen levels in the soil.

“Alfalfa is most common, as well the most productive and easy to establish, legume,” he said.

Other options include red or white clover, birdsfoot trefoil and cicer milkvetch.

He noted that some producers are concerned about bloat in their animals when using legumes in their seed mixture.

“Using a relatively small amount of alfalfa, for example 10 to 20 percent of the forage, minimizes the risk of bloat,” he says.

Birdsfoot trefoil is considered a “safe” legume because it has a high concentration of lignin, which prevents bloat, according to Volesky.

Limited supply

For producers with limited irrigation, switchgrass, big bluestem and Indian grass are appropriate warm-season grasses for an eight- to 12-inch supply of irrigation water. 

Smooth bromegrass, meadow brome, orchard grass and intermediate wheatgrass, along with alfalfa and cicer milkvetch, are appropriate cool-season species.

“In four to eight inches of irrigation water supply, some people tend to favor wheatgrasses because they are known for extensive and deep-rooting systems, as well as for drought tolerance,” Volesky said.

He suggested intermediate wheatgrass, pubescent wheatgrass and alfalfa for this limited water supply.

“Overall, when comparing warm and cool-season characteristics for irrigation, cool-season grasses have the advantage,” says Volesky.

Cool-season varieties have longer growing periods, establish more quickly, generally cost less and typically have a better response to fertilizer, grazing and irrigation water, he noted.

Mixing seasons

“I generally do not favor mixing warm and cool-season grasses,” he continued.

Volesky explained that it presents a challenge in irrigating, fertilizing and grazing.

“Also, the cool-season grasses tend to dominate, over time,” he stated.

Planting separate acres is an option, he continued, suggesting a 25 percent warm-season to 75 percent cool-season ratio of acres. 

He noted that managing this system involves grazing the cool-season grasses in the spring and early summer.

“When the warm-season grasses come up, the producer would rotate over to those acres,” he explained.

Cool-season acres would be again grazed in the fall, when temperatures begin to drop.

“A producer could also rotate over the summer, as needed, to balance the grazing,” Volesky said.

Natasha Wheeler is editor of the Wyoming Livestock Roundup and can be contacted at

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